Abstract Dravet syndrome is an early-onset epileptic encephalopathy characterized by seizures, developmental delay, and cognitive impairment. The disorder results from haploinsufficiency of SCN1A, a neuronal voltage-gated sodium channel gene. The encoded channel, Nav1.1, is an abundant sodium channel in the mammalian nervous system. We propose to investigate the reversibility of prenatal and early postnatal effects of Scn1a haploinsufficiency using a mouse model that recapitulates seizures, behavioral abnormalities, and cognitive impairment. We will use a floxed-stop cassette and an inducible CRE transgene to achieve regulated activation of the transcriptionally inactive targeted Scn1a locus. We will generate the inactive allele, Scn1aFS, by inserting the floxed-stop cassette into intron 1 of Scn1a using CRISPR-Cas9 targeting. The Scn1aFS allele will be activated by tamoxifen-induced expression of an ER-CRE transgene. We will administer tamoxifen to heterozygous Scn1aFS/+ mice at 3 weeks or 6 weeks of age, and assess the effects on seizure onset, seizure susceptibility, and survival. These experiments will provide proof of principle regarding the effectiveness of restoring Scn1a activity for treatment of Dravet syndrome. We will also assess the time window for effective therapy. This work will provide a novel mouse model for future investigations of reversibility of behavioral and cognitive comorbidities, and unique information regarding reversibility of the features of Dravet syndrome as a guide for future therapeutic interventions.